HONG KONG (Reuters) - The most prominent Catholic in greater China warned on Tuesday of violence in Hong Kong next year as a planned campaign of civil disobedience demanding full democracy possibly sparks a backlash from the government after unnerving Beijing.

Cardinal Joseph Zen said he would join the Occupy Central campaign targeting Hong Kong's financial district and would happily risk arrest, saying it was a "desperate last resort".

The 81-year-old former Bishop of Hong Kong said he did not think Beijing would live up to its promises of allowing full democracy in the territory by 2017.

The Hong Kong government and pro-Beijing supporters might try to incite violence to justify a crackdown on a peaceful campaign, he added.

"They may like to provoke some violence, yes, and they may even send people to infiltrate the (protesters). So that's a danger," he told Reuters in an interview. "I'm worried we may finish with some violence ... Then they have the pretext to crush everything."

The former British colony returned to Chinese rule on July 1, 1997, with the promise of universal suffrage as an "ultimate aim" in its mini-constitution, making it potentially the first place on Chinese soil to enjoy fully democratic elections.

The territory enjoys wide-ranging autonomy from Beijing, with a relatively free press, freedom of religion and independent judicial system, but every year, tens of thousands protest to demand full democracy.

The Occupy Central movement is demanding firm government proposals towards electing the city's leader in 2017 and is planning choreographed acts of peaceful disobedience climaxing with a mass rally to shut down the financial district in July next year.

The threats have alarmed Beijing officials and Hong Kong's leader, Leung Chun-ying, has said there is "no possibility" Occupy could be lawful or peaceful, or that it would be tolerated by the police or the courts.

Zen said, however, that Leung's government needed only to "prepare more prisons for the occasion and not prepare tear gas because those people who join Occupy Central are happy to be arrested. They are there in order to be arrested".

Zen also urged Pope Francis to take a tougher line with Beijing.

China's Catholics are divided between the state-sanctioned Catholic Patriotic Association, which has installed bishops without Vatican approval, and an "underground" wing loyal to the Vatican that rejects state control.

"He should not be too nice," Zen said, noting that Pope Francis had yet to send a message to Beijing or appoint a secretary of state for the Holy See. "They don't understand kindness, they only understand force."

Beijing and the Vatican broke off formal diplomatic relations shortly after the Chinese communists took power in Beijing in 1949. (Editing by Nick Macfie)